A gas turbine engine fundamentally consists of one or more compressors, combustion chambers, and one or more turbines, all displaced along an axis of rotation. Shafts connect the turbines to corresponding compressors, thereby providing a mechanism to transmit the mechanical power required to operate the compressor. In many engines, including those used in aircraft, at least one shaft connects one of the turbines to a fan that provides propulsive thrust to the aircraft.
One rare mode of failure in a gas turbine engine is a failure of one or more of the shafts. When one of the shafts fails, the load on the turbine driving the shaft can be substantially reduced, thereby resulting in a turbine overspeed. The turbine overspeed can undesirably result in disc burst or high energy blade release. Accordingly, the industry has developed strategies for addressing the risk of disc or blade release failures subsequent to a shaft failure.
In the past, mechanical and/or electrical sensing techniques have been used to detect a shaft failure. Control mechanisms have been used to cut off the fuel supplied to the engine based on the detected failure. However, care must be taken to ensure that the fuel supply is cut off early enough to avoid or at least substantially reduce the possibility of liberation of high energy debris. Accordingly, early shaft failure detection schemes may be employed. However, because purposely cutting off fuel to an engine is normally undesirable, the engine control systems must not prematurely react before a shaft failure is confirmed. Observable phenomena that occur during shaft failure can also occur due to other factors in which cutting off fuel to the engine would be undesirable.
As a consequence, there is a need for additional protections against high energy debris release upon shaft failure that also reduces the likelihood that the fuel supply is cut off to a healthy engine that has not had a shaft failure.